Local Structure and Energetics of Pr- and La-Doped SrTiO3 Grain Boundaries and the Influence on Core-Shell Structure Formation

Using atomistic simulation techniques, we investigate the structural and energetic effects of Pr- and La-doping on the grain boundaries of SrTiO3. Recent experimental studies have shown that Pr-doping of SrTiO3 produces a large thermoelectric power factor and that this is a result of Pr-rich grain boundaries formed in a coreshell structure. This behavior was not observed for La-doping and dopant-rich grain boundaries were not formed. In this work, for both the infinitely dilute limit and solid solutions with dopant concentrations of up to similar to 15 mol %, Pr-doping at the grain boundaries is found to be far more favorable than doping in the bulk. La-doping at the grain boundaries is also found to be favored over bulk doping, however, to a far lesser extent than that calculated for Pr. The binding energy between Pr ions and charge compensating Sr vacancies is also stronger than for La ion defect clusters. By analyzing the local structures around these defect clusters, we provide possible explanations as to why there is a significant energetic benefit for grain-boundary doping.